In recent years, needs for mounting apparatus for electronic components have been changing from rotary type high-speed mounters to robot type mounters that can flexibly be adapted to various forms of production, in terms of area productivity and component adaptability. Under such circumstances, for more improvement in productivity, those mounting apparatuses of which the number of placement heads to be mounted on one robot has evolved from one to many, and in which a suction nozzle to be used for each placement head is removable and interchangeable, have been forming a mainstream.
In this type of electronic component mounting apparatus, there are some cases to use a so-called multiple board which is prepared by providing a plurality of circuits having an identical pattern on one circuit board, mounting a plurality of electronic components onto this circuit board, and thereafter cutting the board according to individual circuit patterns so that a plurality of sub-boards, each having an identical circuit pattern, are fabricated. It is noted that such a multiple board herein refers to a multiple board composed of a plurality of sub-boards in this Specification.
The following methods are available as examples of prior art for placing electronic components onto such a multiple board composed of a plurality of sub-boards:                (1) A step repeat method including steps of performing a step of placing particular components (hereinafter, referred to as a placement step) onto all the sub-boards, and after completion of the placement step, moving to a next placement step; and        (2) A pattern repeat method including steps of performing all placement steps for one sub-board, and after completion of all the placement steps, moving to a placement step for a next sub-board.        
Both of these step repeat and pattern repeat methods have been widely used since preparing only an NC program as a mounting program for only one sub-board makes it possible to develop a program for all components to be mounted onto a circuit board by setting relative distances to other sub-boards.
A component mounting method for this multiple board is described below.
FIG. 7 shows a mounting procedure for a conventional step repeat method. FIG. 17 sequentially shows a placement procedure through component placement steps with an electronic component mounting apparatus having four placement heads (placement head Nos. 1-4) connected to one another.
In FIG. 17, the column “STEP NO.” shows numbers sequentially assigned to steps of placement, where it is assumed that steps corresponding to a number of placement heads are involved in one-cycle operation from suction to placing of components by the four connected placement heads. The column “SUB-BOARD” shows, by numbers of sub-boards, on which sub-board on the circuit board a component is to be placed. The column “COMPONENT” shows components to be placed during respective steps. The column “PLACEMENT HEAD NO.” shows placement heads to be used during individual steps. The column “SUCTION NOZZLE” shows which type of suction nozzle is used during individual steps. The type of suction nozzle to be used depends on a configuration and size of a component, where suction nozzles come in S (small), M (medium), and L (large) sizes. It is assumed here, as an example, that small-size components are sucked by the S-size suction nozzle, medium-size components are sucked by the M-size suction nozzle, and large-size components are sucked by the L-size suction nozzle. If there are some placement heads that do not suck any component during the one-cycle operation, the placement head actually does not suck and place any component, and so fields of component and suction nozzle are marked with “−” in FIG. 17.
As shown in FIG. 17, during this placement procedure, components of the same type are placed for individual patterns in an order of a chip component C1 of a first pattern to C5 of a second pattern to C9 of a third pattern, . . . , and upon completion of one placement step, a working step moves to a placement step for a next same type of chip components C2, C6, and C10. This placement step is performed for all components. It is noted that the suction nozzle is changed from S size for small-size components to M size for medium-size components after placement of chip component C12 of the third pattern, and changed from M size for medium-size components to L size for large-size components after placement of components SOP1-SOP3 (where “SOP” is an abbreviation of Small Outline Package).
Next, a conventional pattern repeat mounting method is described.
FIG. 18 shows a mounting procedure according to the conventional pattern repeat method. FIG. 19 shows this sequential placement procedure through electronic-component placement steps with an electronic component mounting apparatus having four placement heads (placement head Nos. 1-4).
In this placement procedure, as shown in FIG. 19, after all placement steps for a first pattern are completed in order of chip components C1-C4, SOP1, and QFP1 of the first pattern (where “QFP” is an abbreviation of Quad Flat Package), a working step moves to a placement step for a second pattern. Then, upon completion of placement for the second pattern, the working step moves to a placement step for a third pattern. It is noted that changing of suction nozzles is performed respectively after completion of placement of one kind of component for each pattern. In the case of FIG. 19, changing of suction nozzles is performed three times for each pattern, totaling eight times (a last time being unnecessary).
However, in a case of the step repeat method, since only one, from among the four suction nozzles, is used at all times, component suction and component placement are repetitively performed for every one component, causing mounting time to be prolonged. Thus, this mounting method does not take full advantage of a multiple-head construction having a plurality of suction nozzles, resulting in an inefficient mounting method.
On the other hand, in a case of the pattern repeat method, since changing of suction nozzles is frequently performed, mounting time would be prolonged each time time-consuming nozzle changing work is performed a plurality of times. Thus, this method results in an inefficient mounting method.
Applying such a mounting method to recently increasing large-scale multiple boards composed of, for example, 50-200 boards would cause a mounting apparatus to operate quite tediously. Since such an inefficient mounting method can hardly achieve any improvement in process time, there has been a keen desire for mounting methods of higher efficiency.
Moreover, during suction of electronic components to suction nozzles, even when the electronic components to be sucked are located at adjoining (succeeded) positions of component feeders as shown in FIGS. 20A-20D as an example, transfer heads need to be transferred one by one to perform component suction because an array interval P of component feeders differs from an array interval L of suction nozzles of the transfer heads. Besides, even if the array interval P of component feeders is equal to the array interval L of the suction nozzles, a shift of electronic components from an array line would make it not possible to achieve simultaneous suction. Furthermore, any difference in component thickness would also make simultaneous suction of electronic components no longer achievable.
Therefore, a component placement operation for suction nozzles cannot be performed by a one-time simultaneous vertical operation of the suction nozzles, thereby making it necessary to repetitively perform operations of moving a transfer head to its corresponding component feed position and sucking a component for every suction nozzle as shown in FIGS. 20A to 20D. As a result, it would take a longer time to cause electronic components to be held by the suction nozzles, which has been an obstacle to reduction in mounting time.
The present invention having been achieved in view of these and other issues, an object of the present invention is to provide a component mounting method and a component mounting apparatus which allows mounting time to be shortened by reducing such a suction preparation operation for suction nozzles as suppressing a changing frequency of the suction nozzles, or adjusting intervals of suction nozzles of a transfer head during a process of component mounting onto a multiple board.